Fluid filtration systems are commonly used in today's industrialized society to remove contaminants from a fluid. In one industry in particular, the automotive industry, fluid filtration is essential to ensuring the longevity and proper operation of internal combustion engines. More specifically, it has been found that the normal operation of an internal combustion engine results in the contamination of the lubricating oil and, consequently, increased wear/damage to the engine. Generally, contaminants are introduced into the lubricating oil by five primary sources: engine wear may introduce metal shavings; cylinder blow-by may introduce the products of combustion; water may enter from condensation or a leak in the cooling system; environmental dust may enter through the air intake system; and fuel may enter from fuel system leaks or an excessively rich intake mixture.
Typically, internal combustion engines are provided with a full flow filtration system to remove a portion of these contaminants. However, inasmuch as the full flow filtration system must handle a high rate of lubricating oil, typically in the range of 7 to 10 gallons per minute, the filter must be porous and therefore capable of removing only the larger-sized particulates, such as particulates having a size of 30 to 40 microns or larger. However, it has been found that 92% of all engine wear is the result of particulate matter sized between 7 and 40 microns, the majority of which are not removed by high-capacity full flow filtration systems.
One solution has been to provide a secondary by-pass filtration system that can remove the finer sized particulate matter. In a by-pass filtration system, a fraction of the full flow volume, such as one quart per minute for a 7- to 10-gallon flow rate system, is directed to a by-pass filter system. Typically, the by-pass filtration systems are designed to remove particles down to 1 to 6 microns. To assure maximum pressure differentials across the by-pass filter element, the return oil line is often routed directly back to the oil sump.
Another problem with existing full flow oil filtration systems is that they generally only have sufficient absorbent capacity to absorb a few teaspoons of water. Not only can water aid in the break down of the oil, limiting its lubricating properties, the water may combine with the products of combustion introduced by blow-by. Water mixed with the products of combustion may create sulfuric acid that can pit polished surfaces. In contrast, high-density by-pass filters can absorb substantially greater amounts of water, often a pint or more. When the oil heats up, the water evaporates and is released through the engine's breather conduit(s).
Commonly used by-pass filters are of one of two types. In the first type of by-pass filters, the oil passes through a perforated steel plate where all particles greater than approximately 3 microns are screened and trapped. Other by-pass filters use synthetics, paper, or polyester blends wound around a central core to create a microscopic screen to trap particles. Others use filter mediums constructed from organic materials, such as cotton or paper. While synthetics or organics will theoretically capture minute contaminants equally well, organic filtration often provides superior moisture absorption. As previously discussed, moisture mixed with soot (carbon from blow-by) forms acids. So, organic filtration may offer superior protection by trapping larger amounts of moisture in the filter so acid formation is reduced.
The operation of a typical wound filter media by-pass filter will now briefly be described. Oil at high pressure is injected at a low flow rate to a first end of the filter. The oil runs parallel with the windings between the annulus formed between the inner central core and the outer canister wall. As the lubricating oil travels from the first end to a second end of the filter, contaminants from the oil are removed. Once the oil passes the entire length of the canister, the oil is directed through a central core of the filter to return to the oil sump.
Although existing by-pass filtration systems may be effective, they are not without their problems. Often, the by-pass filters are subject to what is known in the art as channeling, where preferential paths form in the filter media. These preferential paths allow the oil to pass preferentially through the media without significant filtering. Typically, channeling is most pronounced along the inner wall of the canister and along the outer surface of the central core.
Further, changing of the by-pass filter system often results in spillage of the lubricating oil contained within the canister. Not only does the spill create a mess that must be cleaned, it also presents a slipping hazard, may harm the environment, and may lead to the violation of environmental regulations.
Still further, existing by-pass filter systems are subject to substantial pressures over a large surface area. Existing by-pass filter systems often utilize canisters having flat end shapes, which do not efficiently contain the pressure exerted on their surfaces; therefore the canister ends require more material, are heavier, and are more expensive to manufacture.
Thus, there exists a need for a by-pass filter system that reduces channeling, impedes the spillage of oil during removal, and has a canister design that efficiently contains the pressure within the canister.